Method for avoiding pump surges in a compressor

ABSTRACT

A method for avoiding pump surges in a compressor is provided, wherein a plurality of parameters of the compressor are monitored during operation and a desired value range for the plurality of parameters is predetermined, wherein a reaction that counteracts the pump surge is triggered if a number of parameters from the desired value range are exceeded or fallen below. The method also reliably prevents pumping of the compressor during a comparatively high running performance. For this purpose, the plurality of parameters has a parameter assigned to the rotational noise of the compressor.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International Application No. PCT/EP2012/075248 filed Dec. 12, 2012, and claims the benefit thereof. The International Application claims the benefit of European Application No. EP12154644 filed Feb. 9, 2012. All of the applications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention relates to a method for avoiding pump surges in a compressor, in which a plurality of parameters of the compressor are monitored during the operation and a desired value range for the plurality of parameters is predetermined, wherein a reaction that counteracts the pump surge is triggered if a number of parameters from the desired value range are exceeded or fallen below. It further relates to a compressor and a fluid-flow machine having a compressor and a control device which, on the data input side, is connected to a plurality of sensors which are designed to detect parameters during the operation.

BACKGROUND OF INVENTION

Compressors, in particular gas turbines, tend to pump under specific operating conditions. If the back pressure in the direction of flow becomes too high, then the compressor can no longer deliver air and the flow direction reverses locally or even completely. During the local reverse flow, some of the air is caught in the compressor and rotates with the vanes. One speaks of a rotating separation of the flow (rotating stall). On the other hand, in the case of what is known as compressor pumping (deep surge), the medium flows back completely and a violent surge counter to the thrust direction occurs.

Both aerodynamic effects can have serious consequences. While rotating separations can lead to material fractures as a result of severe vibrations, in the case of a pump surge the spontaneous breaking off of entire vanes threatens. In any case, the airflow to the combustion chamber of the gas turbine is interrupted, which leads to the latter shutting down.

The compressor characteristic map, in which typically the pressure ratio between entry and final pressure is illustrated as plotted against the delivery volume, is divided by the pump limit into a stable and an unstable range. Pumping occurs when the operating points of the compressor get into the unstable range as a result of a reduction in the delivery volume (throughput) or as a result of a rise in the final pressure (delivery level).

Usually, in the control electronics or software of a control device of the fluid-flow machine, a pump limit margin which, during operation under design conditions, is sufficiently far removed from the pump limit is defined. Under real conditions, such as with a decreasing mains frequency, high ambient temperatures and/or atmospheric humidities, low heat values of the fuels, but also as a result of ageing of, soiling of or damage to the compressor, it is possible for the pump limit to reach or even fall below the operating characteristic curve. This then leads to the immediate pumping of the compressor.

At the inlet to the compressor (intake cone), one or more sensors equipped as differential pressure switches are frequently installed and, as soon as the flow through the compressor is interrupted during pumping, fall below a specific limiting value and cause the immediate shutdown of the gas turbine by closing the fuel valves. However, the pump protection pressure switches do not detect any approach to the pump limit but prevent only the repeated pumping of the compressor and, possibly, the mechanical damage to the compressor as a result of the immediate interruption to the fuel supply.

In a further development, a compressor pressure ratio limiting controller is therefore frequently also employed. A controller of this type considers parameters of the compressor (pressure ratio, mains frequency, pre-rotation vane position and ambient conditions such as temperature and atmospheric humidity) and compares these with permissible values from a compressor-specific pump limit characteristic map. If the current operating point approaches the pump limit, that is to say when a predefined desired value range is exceeded or fallen below, a reaction counteracting the pump surge is triggered.

However, the disadvantage with both the aforementioned methods is that they do not take into account any ageing of, massive soiling of or damage to the compressor, and thus, with increasing running time of the fluid-flow machine, are no longer reliably able to prevent pumping of the compressor.

Furthermore, for example from US 2009/0055071 A1, it is known to arrange pressure sensors and/or microphones in a chamber upstream of the burner, detecting the states of the compressed air in the chamber. The signals from these are then evaluated in order to analyze an impending pump event. Likewise, EP 2 375 081 A2 proposes using shockwaves and other acoustic phenomena of the compressed air for pump prediction. Here, too, microphones or similar pressure sensors are employed. However, it is disadvantageous that sensors of this type have only a limited service life at relatively high ambient temperatures.

SUMMARY OF INVENTION

The invention is therefore based on an object of specifying a method for avoiding pump surges in a compressor, a compressor and a fluid-flow machine which, even at a comparatively high operational performance, reliably prevent pumping of the compressor.

With respect to the method, this object is achieved, according to aspects of the invention, by the plurality of parameters comprising a parameter assigned to the rotational noise of the compressor.

Here, aspects of the invention are based on the consideration that, for reliable avoidance of pump surges, even at a relatively high operational performance of the fluid-flow machine, there should be no recourse exclusively to previously defined characteristic maps and controllable operating variables but instead current measured variables suitable for the preventative detection of an imminent pump surge should be used. Predictive detection would be possible if, by means of appropriate measurements, an approach to the pump limit in the form of the rotating stall, i.e. the rotating flow separation, could already be detected. Here, it has been detected that a flow separation of this type generates vibrations in the compressor stages, which lead to increased pressure pulsations and further vibrations. These pressure pulsations and vibrations change the rotational noise of the compressor, so that a change in the rotational noise accordingly indicates imminent pumping in a predictive manner. Therefore, a parameter assigned to the rotational noise of the compressor should be measured and used to avoid pump surges.

In order to detect a change in the rotational noise, numerous parameters and numerous sensors which are capable of indicating vibrations in the compressor can be used. For instance, it is possible to use highly dynamic pressure sensors, with which the pressure pulsations described can be detected. However, the disadvantage here is that pressure sensors of this type are not stable in the long term and are not suitable for all the operating conditions of the fluid-flow machine (increased soiling, humidity, increased humming, compressor washing, etc). Therefore, the measured parameter assigned to the rotational noise of the compressor is advantageously a vibration amplitude and/or frequency of a component of the fluid-flow machine. This is because the pressure pulsations are also transmitted to the components of the fluid-flow machine. Thus, the rotational noise can be determined via the mechanical vibrations of appropriate components of the gas turbine. Here, the sensors and transmitters suitable for the purpose are insensitive to the aforementioned operating conditions and are therefore longer-lasting.

Advantageously, the component provided with the appropriate sensors is the shaft and/or the housing of the turbine and/or of the compressor. By using the housing and/or shaft vibrations of turbine and/or compressor, the rotational noise can be determined particularly well, in particular with regard to an imminent approach to the pump limit.

Advantageously, the parameters used further comprise the shaft rotational speed, the compressor final pressure and/or the pre-rotation vane position. As a result, the predictive detection of the pumping can be improved further, since the rotational noise can be determined particularly well with the aid of these additional parameters, for example by using specific evaluation algorithms in a computer specifically provided for the measurement.

In a particularly advantageous refinement, the reaction counteracting the pump search comprises a reduction in the desired value of the turbine outlet temperature and/or a reduction in the fuel mass flow. Within the context of regulating the fluid-flow machine, the consequence of reducing the desired value of the turbine outlet temperature is that the adjustable pre-rotation vanes of the compressor are opened. As a result, the margin from the pump limit increases. By means of a reduction in the fuel mass flow, the compressor pressure and therefore the compressor pressure ratio is reduced as quickly as possible. As a further measure, air can be removed, for example via the anti-icing valve of the compressor at the compressor end. In an improving manner, the air removal via the anti-icing valve can then be introduced at the compressor inlet again. As a result, the compressor pressure ratio is likewise reduced.

Advantageously, a fluid-flow machine having a compressor and a control device is designed to carry out the method described.

With respect to the fluid-flow machine having a compressor and a control device which, on the data input side, is connected to a plurality of sensors which are designed to detect parameters during the operation, the object is achieved in that one of the sensors is designed to detect a parameter assigned to the rotational noise of the compressor.

Here, the respective sensor is advantageously a vibration sensor. This is advantageously configured as a vibrometer. Particularly advantageous here are vibrometers which measure accelerations on a piezoelectric basis, such as, for example, the piezoelectric accelerometer CA 901 from the Meggitt company. This is particularly long-lasting and robust with respect to high temperatures, soiling and during compressor washing.

In an advantageous refinement, the respective sensor is assigned to the shaft and/or the housing of the turbine and/or of the compressor. Here, appropriate sensors are advantageously fitted at multiple points on the circumference of the compressor, ideally in holes for radial measurement equipment on the outside, i.e. not in the flow path.

A power plant advantageously comprises a fluid-flow machine as described.

The advantages achieved by the invention comprise in particular in the fact that, as a result of the specific measurement of the rotational noise of the compressor of a fluid-flow machine, an approach to the pump limit or a rotating stall can be detected before actual pumping occurs. This can be achieved particularly simply by means of appropriate vibration transmitters which measure pressure changes of rotating compressor rotor blades of a stage. With the aid of other transmitters (shaft rotational speed, compressor final pressure, pre-rotation vane position), the rotational noise of the compressor can be determined in a control device such as, for example, a computer with specific evaluation algorithms.

This also makes it possible to detect foreign bodies, which could lead to damage to the compressor flow path and parts thereof. This is because foreign bodies of this type also lead to a change in the rotational noise. Consequential damage to components downstream of the compressor can thus be avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail by using a drawing. In the latter, the FIGURE shows, schematically, a section through the upper half of a compressor of a gas turbine.

DETAILED DESCRIPTION OF INVENTION

The fluid-flow machine 1 illustrated as an extract in the figure is configured as a gas turbine. Of the gas turbine, only the compressor 2 is shown. The compressor 2 comprises guide vanes 6 fixed to a housing 4 and therefore stationary, which are located in a flow duct 8 between compressor inlet 10 and compressor outlet 12. The first guide vane 6 in the flow direction of the air is configured as an adjustable pre-rotation vane 14. As a result, the supply of air into the flow duct 8 can be regulated and throttled.

After each guide vane 6, 14 in the flow direction of the air, rotor blades 18 are respectively arranged on a shaft 16. The rotor blades 18 and the guide vanes 6, 14 are respectively arranged in the manner of stars in rings in the flow duct 8. A ring of guide vanes 6, 14, together with the ring of rotor blades 18 following in the flow direction, respectively forms a stage of the compressor 2.

For the purpose of early detection of imminent pumping, a multiplicity of sensors, not illustrated in detail, are arranged in the compressor 2. In particular, vibration sensors 20 configured as piezoelectric acceleration sensors are arranged in holes for radial measurement equipment, respectively arranged at 90°, which detect mechanical vibrations and therefore permit an image of the rotational noise of the compressor 2.

The rotational noise is determined by means of an evaluation algorithm 22, which is implemented as software on a control device, for example a computer, not specifically illustrated. Input into the evaluation algorithm, besides the vibration data from the vibration sensors 20, is the data from further corresponding transmitters and sensors. These include the shaft rotational speed, the compressor pressure ratio between compressor inlet 10 and compressor outlet 12, the pre-rotation vane position, the shaft vibration and the housing vibration on compressor and turbine.

If, because of the approach to the pump limit, the rotational noise or the vibratory mode of the vibration measuring instruments present changes, the computer sends signals (binary or analog) in order to carry out appropriate reactions which prevent pumping.

Reactions comprise the opening of the anti-icing valve 24, the lowering of the turbine outlet temperature 26 and the reduction in the quantity of fuel 28. Further measures can also be provided. The reactions can be triggered in accordance with need, depending on the results determined by the evaluation algorithm 22. For instance, it is possible for only individual reactions from those mentioned above to be carried out or else a plurality thereof. Furthermore, messages can be given to operating personnel 30.

Should a foreign body fly through the flow duct 8 of the compressor 2, this can likewise be established via the change in rotational noise. Foreign body impacts likewise trigger messages to the operating control technology or to the operating personnel 30. The operating control technology or the personnel can then decide about the measures to be taken, for example removal and inspection of the compressor 2 or the fluid-flow machine 1. Foreign body impacts which lead to secondary damage or can cause damage to compressor components can thus be detected and reported—provided that they do not occur spontaneously. Spontaneously occurring severe damage, on the other hand, leads to automatic measures under FOD 32 (Foreign Object Detection), such as the shutdown of the gas turbine. 

1.-13. (canceled)
 14. A method for avoiding pump surges in a compressor, comprising: monitoring a plurality of parameters of the compressor during the operation and predetermining a desired value range for the plurality of parameters, triggering a reaction that counteracts an imminent pump surge if a number of parameters from the desired value range are exceeded or fallen below, wherein the plurality of parameters comprises a parameter assigned to rotational noise of the compressor, and the parameter assigned to the rotational noise of the compressor is a vibration amplitude and/or frequency of a component of a fluid-flow machine, and the component is a shaft and/or a housing of the compressor, and detecting mechanical vibrations with sensors fitted at multiple points on the circumference of the compressor.
 15. The method as claimed in claim 14, wherein, in order to determine the rotational noise, accelerations of the component are detected.
 16. The method as claimed in claim 14, wherein the plurality of parameters comprises shaft rotational speed, compressor final pressure and/or pre-rotation vane position.
 17. The method as claimed in claim 14, wherein the reaction counteracting the pump surge comprises a reduction in the desired value of turbine outlet temperature and/or a reduction in fuel mass flow.
 18. The method as claimed in claim 14, wherein the compressor is part of a fluid-flow machine.
 19. A compressor, comprising: a control device, which, on the data input side, is connected to a plurality of sensors which are designed to detect parameters during the operation, wherein the plurality of sensors are designed to detect a parameter assigned to the rotational noise of the compressor, wherein the plurality of sensors are vibration sensors which are arranged on the compressor of the gas turbine and determine mechanical vibrations of the components, and wherein the sensors are arranged at multiple points on the circumference of the compressor.
 20. The compressor as claimed in claim 19, wherein the plurality of sensors are configured as acceleration sensors.
 21. A fluid-flow machine having a compressor as claimed in claim
 19. 22. A power plant having a fluid-flow machine as claimed in claim
 21. 